In the recovery of oil from subterranean, oil-bearing formations, it is only possible to recover a portion of the original oil present in the reservoir by primary recovery methods which utilize the natural formation pressure or pumps to produce the oil through suitable production wells. For this reason, a variety of enhanced recovery techniques have been developed which are directed either to maintaining formation pressure or to improving the displacement of the oil from the porous rock matrix. Steamflooding is a well-known, enhanced recovery technique. Several types of steamflooding methods are known. In the widely used steam-soak process, steam is injected into one well and oil is produced from the same well. During the steam injection stage of the steam-soak method, an oil bank forms ahead of the steam front and is driven away from the injection well. During the production stage of the steam-soak method, where some flashing of hot water to steam occurs, all fluid flow and heat flow are directed towards the section of the reservoir containing the least amount of oil, i.e. the well into which the steam has been injected and from which the oil must now be recovered.
Multi-well steamflooding processes are also known wherein steam is introduced into the oil-bearing reservoir through means of an injection well and is recovered from one or more production wells located at a distance from the injection well. In such known, conventional steamflooding processes, an external source of steam, such as a boiler, is used continuously as the source of steam injected into the injection well and is the only means of steam propagation throughout the reservoir. That is, steam is injected through the injection well at a continuous pressure and this pressure is used as the driving force to move oil through the oil-bearing reservoir and to subsequent removal through the production well.
The present invention is directed to a novel steamflooding process which is cost-effective when compared with conventional steamflooding or steam-soak processes by either producing more oil with the same amount of heat input or by producing the same amount of oil with a lesser quantity of steam.